A. Field of the Invention
The present invention relates to a method for checking an optical security feature in or on a portion of a value document on the basis of pixel data of an image of the portion, to a method for checking an optical security feature of a value document, and to an apparatus for checking an optical security feature of a value document.
B. Related Art
Value documents are understood here to be card- and preferably sheet-shaped objects that represent for example a monetary value or an authorization and hence should not be producible arbitrarily by unauthorized persons. They hence have security features that are not simple to produce, in particular to copy, whose presence is an indication of authenticity, i.e. manufacture by an authorized body. Important examples of such value documents are identity documents, chip cards, coupons, vouchers, checks and in particular bank notes.
Of special interest are optical security features, which are understood within the framework of the present invention to be security features of a value document that show characteristic optical properties upon interaction with optical radiation, i.e. electromagnetic radiation in the infrared, ultraviolet or visible spectral region. The optical properties can be in particular remission properties and/or transmission properties and/or luminescence properties.
Certain types of security features, hereinafter also designated as human features, are intended to be checkable for authenticity without any technical aids. Examples of such security features are in particular so-called OVD features, which will hereinafter be understood to be security features that show viewing angle-dependent visual effects or whose optical properties, for example the color, depend on the viewing angle. Such security features can convey a different pictorial impression to a viewer from different viewing angles, showing for example a different color impression or brightness impression and/or a different graphic motif depending on the viewing angle.
Value documents having such optical security features must be checked by machine for whether they are authentic. Because forgeries of value documents are becoming ever better in the course of time, it is necessary to improve the check of the authenticity of security features on value documents ever further. In so doing, the complexity of the equipment should be kept low, however.